Superimposed modular construction of vaporizable patterns

ABSTRACT

Vaporizable patterns of substantial depth and/or complexity are carved in modules by tape-controlled milling machines. The modules have abutting edge surfaces into which oversize bisymmetrical dovetail splines of the same material are inserted. A standard depth for the modules is the working length of rotating cutter tools. The partial elasticity of the material makes assembly possible and gives the joint bend resistance to exclude foundry sand.

United States Patent Parsons [451 Dec. 26, 1972 [54] SUPERIMPOSEDMODULAR CONSTRUCTION OF VAPORIZABLE PATTERNS [72] Inventor: John T.Parsons, 205 Wellington,

Traverse City, Mich. 49684 22 Filed: Sept. 25, 1970 211 App]. No.:75,538

Related U.S. Application pm [63] Continuation-in-part of Ser. Nos,867,980, Oct. 20, 1969, Pat. No. 3,635,124, and Ser. No. 874,930,

Nov. 7, 1969, Pat. NO. 3,625,280.

[52] US. Cl. ..29/407, 29/451, 29/525,

[51] Int. Cl. ....B23q 17/00, 823p 11/02, 1323p 19/02 [58] Field ofSearch ..29/406, 446, 164, 407, 451,

[56] References Cited UNITED STATES PATENTS 7 1,814,678 7/1931 Ferguson..29/446 3,172,932 3/1965 Heyden' ..29/446 3,269,424 8/1966 Fisher..29/446 Primary Examiner-Thomas H. Eager Attorney-Jerome A. Gross 571ABSTRACT Vaporizable patterns of substantial depth and/or complexity arecarved in modules by tape-controlled milling machines. The modules haveabutting edge surfaces into which oversize bi-symmetrical dovetailsplines of the same material are inserted. A standard depth for themodules is the working length of rotating cutter tools. The partialelasticity of the material makes assembly possible and gives the jointbend resistance to exclude foundry sand.

6 Claims, 4 Drawing Figures SUPERIMPOSED MODULAR CONSTRUCTION OFVAPORIZABLE PATTERNS CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation-in-part of my copending applicationsentitled Use of Tape-Controlled Milling Machines to Carve CombustibleCasting Patterns, Ser. No. 867,980, filed Oct. 20, 1969, Pat. No.3,635,124, and Self-Aligned Multi-part Combustible Casting Pattern andMethod of Making Same, Ser. No. 874,930, filed Nov. 7, 1969, U.S. Pat.No. 3,625,280; and to the extent of the disclosure of common subjectmatter, priority is claimed as of the filing dates of said applications.

BACKGROUND OF THE INVENTION This invention relates to methods of formingvaporizable patterns by machine carving, especially using programmedmachine tools. It is particularly applicable to making patterns whosetotal depth exceeds the working length of rotating cutters available formachining, and to constructing hollow patterns which could not bemachined in a single piece.

vaporizable patterns have been used in foundries for the formation ofmetal castings for a number of years. In one conventional practice,shown in US. Pat. to Shroyer, No. 2,830,343, foundry sand is packedabout such patterns and about a pouring gate leading thereto and themolten metal is cast without removing the pattern. The heat of the metalvaporizes the pattern material as the 'molten metal descends from thegate to and through the pattern form, replacing the pattern materialwith metal.

Conventionally such patterns are formed by building up segments cut fromblocks or slabs of low density polystyrene, using procedures similar tothose used in the making of wood patterns. The several pieces areassembled usually by gluing, and fillets of wax are wiped into thejoints. This method of assembly is disadvantageous, especially when thepattern is hollow and box-like. The glued joint may separate under theforces of packing sand, either failing completely or admitting sandparticles into the joint. Further, since glue and wax do not vaporizecompletely at the same low temperature as the polystyrene, these too mayform inclusions in the casting.

The general purpose of the present invention is to provide a method ofassembling modules of machinecarved vaporizable patterns. Other purposesinclude machine carving of combustible patterns of greater depth andcomplexity than would otherwise be feasible. Further purposes willbeapparent from the detailed disclosure hereof.

SUMMARY OF THE INVENTION The present invention is advantageously used incarving and assembling those vaporizable patterns whose depth exceedsthe available working length of rotating cutters of a machine tool, andalso those whose complex form makes necessary their carving in modules.In the preferred form of invention, I first establish a standard depthto whichmodules of the pattern may be carved, which depth is no greaterthan the working length of the rotating cutters. I divide the overallform of the pattern into a plurality of modules whose depth equals or isno greater than this standard depth. Using square cut slabs of expandedvaporizable material whose depth equals this standard depth, insertedinto the machine tool so that the cutter axis will be aligned in thedirection of the depth, I carve each module, and provide square cutmating surfaces. I then machine undercut grooves in the mating surfaces,in alignment with corresponding grooves vof adjacent modules. Aftermasking the mating surfaces including the grooves, I spray the exposedsurfaces with a ceramic material. Then removing the masking, I pressfit, into I BRIEF DESCRIPTION OF THE DRAWINGS I FIG. 1 is a fragmentaryperspective view showing the carving of a lower module of a multi-partvaporizable pattern according to the method of the present invention.

FIG. 2 is an exploded perspective view showing steps in the assembly ofthe lower pattern module of FIG. 1,

an intermediate module, and an upper module similarly carved.

FIG. 3 is an enlarged fragmentary view taken along line 3-3 of FIG. 2,also showing a groove cutter removed upwardly.

FIG. 4 isan enlarged fragmentary sectional view taken along line 4-4 ofFIG. 2 and showing a typical section of a pattern wall joint, in whichthe dashed lines show a grooved lower wall of the intermediate module ofFIG. 2 when assembly is completed.

DESCRIPTION OF THE PREFERRED EMBODIMENT In this embodiment, I illustrateand describe procedures for carving a polystyrene pattern whose totaldepth is three times the standardized depth d of large carving cuttersof a milling machine, such as the rotatable cutter generally designatedb. To achieve a pattern of this total depth requires three modules ofdepth d; these include a lower module generally designated 10, anintermediate module generally designated 11 and an upp r modulegenerally designated 12. As shown in FIG. 2, the depth of each moduleequals the depth d of the cutter b. Each of the modules 10, l1 and 12 iscarved from a square cut slab of vaporizable pattern material,preferably expanded polystyrene whose density is in a range between 1and 1% pounds per square foot. Such material is partially elastic andhence well adapted for assembly in the manner hereinafter set forth. Useof slabs whose upper and lower surfaces are square cut to define theprecise depth d simplifies carving and assures precise abutting fit onassembly of the modules.

In carrying out the present process the first step is to carve theindividual modules 10, 11 and 12. Only the right end of each module isillustrated. Using the rotating milling cutter b, the entire outersurface 14 of the lower module is carved to desired contour around itsentire periphery, preferably using a tape controlled milling machine inthe manner taught by my said copending application Ser. No. 867,980, US.Pat. No. 3,635,124 entitled Use of Tape Controlled Milling Machines toCarve Combustible Casting Patterns; and its entire inner surface 15,including the fillets and cutout illustrated, is carved by the sameprocedure. Similarly the entire outer surfaces 16 and inner surfaces 17of the intermediate module 11 are carved, the milling machine being soprogrammed as to bring about precise alignment of its vertical wallportions with those of the lower module 10. Likewise the upper module 12is carved to provide vertical walls with aligned outer surfaces 18 andinner surfaces 19, as well as an inner top wall 20. I

Where the total pattern depth is not an even multiple of the standarddepth d of the rotating cutters b, programming of the milling machinemay be facilitated by utilizing such standard depth for all but one ofthe pattern modules, but this may not be feasible, for example, whereinternal portions of the pattern are so complex as to require carving inseparate pieces of lesser depth. In this event, their upper and lowerwall edge surfaces will be square cut horizontally.

On assembly the adjacent square cut edge surfaces of the pattern modules10, 11 and 12 are to abut and mate. Thus, the top edge surface 21 of thelower module 10 will be presented abuttingly against the lower edge 22of the intermediate module 11, and its upper edge 23 will similarly abutthe lower edge surface 24 of the upper module 12.

In order to complete each module and mate these abutting surfaces,aligned grooves are cut into them. Three such grooves, each generallydesignated 25, are shown in FIG. 1 cut into the upper surface 23 of thelower module 10. A groove cutterf, shown in'FlG. 3, has radial cuttingblades g which are flat along their undersurfaces taper narrowinglyupwards. To cut .the grooves 25 the cutter f is forced downwardly,-as itrotates, ata point between the ends of the desired length k of thegroove, forming a cylindrical groove portion 26, shown in cross-sectionin FIG. 3, whose diameter equals that of the greatest diameter of thetapering cutter f. The cutter is then moved longitudinally in bothdirections within the wall in which the groove is to be cut, forming anundercut groove or dovetail 25 whose bottom surface 27 is equal in widthto the greatest diameter of the cutter f and whose walls taper inwardly,according to the conformation of the cutter blades g, to a lesser topgroove width 28.

By the length k of the groove 25 is meant the length due tolongitudinal, movement of the shaft of the cutter f, without takingaccount of semi-circular rounded end portions 29 which are unavoidablyleft, due to the radius of the cutter f.

, The undercut grooves 25 in the mating surface 21 of the lower module10 may be located at positions convenient for joining, taking intoconsideration wall thickness available in the module 10 and in theundersurface of mating portions of the intermediate module 1 l, in whichsimilar grooves 30 are cut in precise alignment. Likewise, similarundercut grooves generally designated 31 are cut in the upper matingsurface 23 of the intermediate module 1 l, and corresponding alignedgrooves 32 are cut in the lower mating surface 24 of the upper module12, all as shown in FIG. 2.

In the use of expanded polystyrene patterns in sand molds, it isconventional to spray coat their outer surfaces with a ceramic coating.With any modular construction of patterns, a problem is presented how toexclude such coating from the mating surfaces 21, 22, 23, and 24 or inthe grooves 25, 30, 32; ceramic material in these places would forminclusions in the casting when the pattern material was vaporized bymolten metal.

With the present construction, this problem is readily solved. Ordinarymasking tape 34 is utilized to cover these surfaces and the groovestherein, prior to spraying such ceramic coating. Once spray coated, themasking tape 34 is peeled off, as shown in F IG. 2.

Assembly splines generally designated 35 shown in FIGS. 2 and 4,previously formed and cut to the length k, are then press fitted intothe grooves 25 in one of each pair of mating surfaces; F IG. 2 shows twoof them in the grooves 25 of the surface 21 of the lower module 10. Theassembly splines 35 are formed of the same partially elastic low densityvaporizable material as the pattern modules 10, 11 and 12. They may beformed initially as a long strip of double dovetailed cross-section, asseen in the explodedperspective FIG. 2, and then cut to the length k.Considering the cross-section, its width at its mid-height correspondsgenerally to the top groove width 28; it tapers to broader top andbottom edges whose width may substantially equal the bottom width 27 ofa groove 25. The partial elasticity of the material permits pressfitting the splines 35 into the grooves 25 without maintaining precisetolerances.

' Since the preferred expanded polystyrene plastic material is alsosubject to partial permanent set when compressed, this may becompensated for by using splines 35 which are slightly oversize andwhose top and bottom edges may be rounded to facilitate press fitting. 7

Patterns made in modules and assembled in accordance with the presentinvention must have adequate strength and bend resistance as to assureagainst the entrance of sand particles into the joints when foundry sandis packed against them. Where the pattern walls are relatively slendercompared with their height, it may be necessary to provide longcontinuous grooves 25 and splines 35 therein to lock the mating wallportions together over the entire lengths of the mating surfaces. In thepresent invention this'offers no difficulty; strips of spline materialare cut to whatever length the grooves k have been carved.

Several advantages of the present construction are worthy of specialmention. The modules 10, 11 and 12, being of a standard depth or less,are readily handled during shipment to the foundry. Prior to shipment,they may be masked and sprayed; as the ceramic coating hardens, itstrengthens the vaporizable material. Then,

after shipment to the foundry, the masking is removed and the splineinsertion and assembly operations may be performed. In contrast to thepossible alternative of assembly of pattern modules by tongue and grooveconstruction, there are here no projecting tongue portions which mightbreak in handling and would be difficult to mask off prior to spraying.These advantages make the present construction uniquely valuablewherever patterns are made in modules and assembled at the foundry. I

In case of patterns which, like the pattern as illustrated, are deep,box-like, or both, the sand may bev packed about the lower module beforeits masking tape 34 is removed; and the spline insertion and assemblymay thus progress one module at a time, as the sand is packed,successively about each. This permits the construction, integrally, ofcastings which might not be easily made by any prior known process.

In certain patterns, the location of hubs bosses and other complicatingfeatures may require zig-zag or irregular mating surfaces of portions ofthe modules. Carving the pattern form by first dividing it intoirregular modules whose boundaries permit the machine carving of suchbosses and hubs, and then assembling the pattern as taught herein,permits casting complex forms to substantially final configuration, sothat only a minimum of subsequent machining is required.

I claim:

I. A method of constructing multi-part vaporizable patterns, consistingof the steps of carving from vaporizable partially elastic patternmaterial a first and a second pattern module with mating surfacesadapted to abut each other,

cutting in the mating surfaces of each module a lengthwise under-cutgroove spaced to align with a corresponding groove in the mating surfaceof the other module,

press fitting, into the groove of one module, one half of an oversizebi-symmetrical spline of the same material and having such form as willengage within the undercut of said groove,

press fitting the groove of the other pattern module over the other halfof the dovetail spline projecting from said mating surface,

whereby the partial elasticity of the material will hold the matingsurfaces in abutment in a sealed bendresistantjoint.

2. A method of constructing hollow patterns for castings, consisting ofthe steps of v carving out the interior portion of a solid slab ofvaporizable pattern material to leave an outer wall terminating in asquare cut mating surface, thereby to provide a first pattern module,

carving from the same material a second pattern module including analigned wall terminating in a square cut mating surface adapted to abutthe mating surface of the first module,

cutting in the mating surfaces of each module an undercut groove spacedto align with a corresponding groove in the mating surface of the othermodule, and

press fitting, into the groove of one module, one

dovetail side of an oversize bi-symmetrical spline of the same material,

whereby the partial elasticity of the material will hold the matingsurfaces in a sealed bend-resistant joint.

3. A method of machine carving and assembling vaporizable patterns whosedepth exceeds the available working length of rotating cutters of amachine tool, comprising the steps of I establishing a standard depth towhich modules of such pattern may be carved, which depth is no greaterthan such working length of the rotating cutters,

dividing the overall form of the pattern into a plurality of moduleswhose depth equals or is no greater than said standard depth, carvingsquare cut slabs of expanded, partially elastic, vaporizable patternmaterial of such standard depth to form such pattern modules by rotatingsuch cutters on axes aligned in the direction of said depth, andproviding square cut mating surfaces on adjacent modules, machiningundercut grooves in said mating surfaces in alignment with thecorresponding grooves in the mating surfaces of adjacent modules, pressfitting, into the grooves in one module, one dovetail side of anoversize bi-symmetrical spline of the same partially elastic material,and press fitting the groove-of a second module elastically over saidother dovetail side of the spline, whereby the partial elasticity of thematerial will hold the mating surfaces in a sealed bend-resistant joint.4. The method as defined in claim 3, together with the intermediatesteps, performed after carving the modules and machining their grooves,of masking said grooved mating surfaces, spraying a ceramic coating onthe unmasked surfaces, and then removing the masking, all prior to thedefined press fitting steps. 5. A method of machine carving andassembling vaporizable patterns whose depth exceeds the availableworking length of rotating cutters of a machine tool, comprising thesteps of establishing a standard depth to which modules of such patternmay be carved, which depth is no greater than such working length of therotating cutters, dividing the overall form of the pattern into aplurality of modules whose depth equals or is no greater than saidstandard depth, carving square cut slabs of expanded, partially elastic,vaporizable polystyrene pattern material of such standard depth toform'such pattern modules by rotating such cutters on axes aligned inthe direction of said depth, and providing square cut mating surfaces onthe modules to be mated to eachother, machining grooves in said matingsurfaces in alignment with the corresponding grooves in the matingsurfaces of the adjacent modules, masking said grooved mating surfaces,applying a pattern coating onto the pattern modules about the surfaceportions so masked, removing the masking, press fitting, into thegrooves in one module, one half of an oversize bi-symmetrical spline ofthe same partially elastic material, and press fitting thegroove of asecond module elastically onto said other half of the spline until themating surfaces abut each other, whereby the uncoated mating surfaceswill be held sealed in a bend-resistant joint. 6. A method of machinecarving and assembling vaporizable patterns comprising the steps ofdividing the overall form of the pattern into a plurality of modules,

removing the masking, press fitting, into the groovesin one module, oneportion of an oversize spline of the same partially elastic material,and press fitting the groove of a second module elastically onto saidother half of the spline until the mating surfaces abut each other,whereby the uncoated mating surfaces will be held sealed in abend-resistant joint.

* 10K IIK

1. A method of constructing multi-part vaporizable patterns, consistingof the steps of carving from vaporizable partially elastic patternmaterial a first and a second pattern module with mating surfacesadapted to abut each other, cutting in the mating surfaces of eachmodule a lengthwise under-cut groove spaced to align with acorresponding groove in the mating surface of the other module, pressfitting, into the groove of one module, one half of an oversizebi-symmetrical spline of the same material and having such form as willengage within the undercut of said groove, press fitting the groove ofthe other pattern module over the other half of tHe dovetail splineprojecting from said mating surface, whereby the partial elasticity ofthe material will hold the mating surfaces in abutment in a sealedbend-resistant joint.
 2. A method of constructing hollow patterns forcastings, consisting of the steps of carving out the interior portion ofa solid slab of vaporizable pattern material to leave an outer wallterminating in a square cut mating surface, thereby to provide a firstpattern module, carving from the same material a second pattern moduleincluding an aligned wall terminating in a square cut mating surfaceadapted to abut the mating surface of the first module, cutting in themating surfaces of each module an undercut groove spaced to align with acorresponding groove in the mating surface of the other module, andpress fitting, into the groove of one module, one dovetail side of anoversize bi-symmetrical spline of the same material, whereby the partialelasticity of the material will hold the mating surfaces in a sealedbend-resistant joint.
 3. A method of machine carving and assemblingvaporizable patterns whose depth exceeds the available working length ofrotating cutters of a machine tool, comprising the steps of establishinga standard depth to which modules of such pattern may be carved, whichdepth is no greater than such working length of the rotating cutters,dividing the overall form of the pattern into a plurality of moduleswhose depth equals or is no greater than said standard depth, carvingsquare cut slabs of expanded, partially elastic, vaporizable patternmaterial of such standard depth to form such pattern modules by rotatingsuch cutters on axes aligned in the direction of said depth, andproviding square cut mating surfaces on adjacent modules, machiningundercut grooves in said mating surfaces in alignment with thecorresponding grooves in the mating surfaces of adjacent modules, pressfitting, into the grooves in one module, one dovetail side of anoversize bi-symmetrical spline of the same partially elastic material,and press fitting the groove of a second module elastically over saidother dovetail side of the spline, whereby the partial elasticity of thematerial will hold the mating surfaces in a sealed bend-resistant joint.4. The method as defined in claim 3, together with the intermediatesteps, performed after carving the modules and machining their grooves,of masking said grooved mating surfaces, spraying a ceramic coating onthe unmasked surfaces, and then removing the masking, all prior to thedefined press fitting steps.
 5. A method of machine carving andassembling vaporizable patterns whose depth exceeds the availableworking length of rotating cutters of a machine tool, comprising thesteps of establishing a standard depth to which modules of such patternmay be carved, which depth is no greater than such working length of therotating cutters, dividing the overall form of the pattern into aplurality of modules whose depth equals or is no greater than saidstandard depth, carving square cut slabs of expanded, partially elastic,vaporizable polystyrene pattern material of such standard depth to formsuch pattern modules by rotating such cutters on axes aligned in thedirection of said depth, and providing square cut mating surfaces on themodules to be mated to each other, machining grooves in said matingsurfaces in alignment with the corresponding grooves in the matingsurfaces of the adjacent modules, masking said grooved mating surfaces,applying a pattern coating onto the pattern modules about the surfaceportions so masked, removing the masking, press fitting, into thegrooves in one module, one half of an oversize bi-symmetrical spline ofthe same partially elastic material, and press fitting the groove of asecond module elastically onto said other half of the spline until themating surfaces abut each other, whereby the Uncoated mating surfaceswill be held sealed in a bend-resistant joint.
 6. A method of machinecarving and assembling vaporizable patterns comprising the steps ofdividing the overall form of the pattern into a plurality of modules,carving expanded, partially elastic, vaporizable polystyrene patternmaterial to form such pattern modules, and providing square cut matingsurfaces on the modules, to be mated to each other, machining grooves insaid mating surfaces in alignment with the corresponding grooves in themating surfaces of the adjacent modules, masking said grooved matingsurfaces, applying a pattern coating onto the pattern modules about thesurface portions so masked, removing the masking, press fitting, intothe grooves in one module, one portion of an oversize spline of the samepartially elastic material, and press fitting the groove of a secondmodule elastically onto said other half of the spline until the matingsurfaces abut each other, whereby the uncoated mating surfaces will beheld sealed in a bend-resistant joint.